Arm structure for an industrial robot

ABSTRACT

An arm structure for an industrial robot, comprising a first robot arm (16) supported on top of a vertical robot shaft (14), and a second robot arm (20) pivotally joined through a transmission-reduction gear box (18) to the free end of the first robot arm (16). A plurality of coupling bolts (22) are extended through the interior of the first robot arm (16), each coupling bolt (22) has one end (22b) fastened to the flange (18b) of the transmission-reduction gear box (18) and the other end (22a) projecting from and fastened to the rear end of the first robot arm (16). Fastening nuts (24) each engage at least one end (22a or 22b) of each coupling bolt (22) to couple the first robot arm (16) and the transmission-reduction gear box (18) so as to preload the first robot arm (16) by a compressive force.

DESCRIPTION

1. Technical Field

The present invention relates generally to an arm structure for themovable unit of an industrial robot and, more particularly, to anindustrial robot comprising an effective and inexpensive mechanism forimproving the load capacity of the arm structure thereof in conveying aweight such as a workpiece held by a robot hand attached to theextremity of the arm structure or in executing robot work in a loadedstate with a tool held by the robot hand.

2. Background Art

In a horizontal multi-articulate type robot applied to precisionassembling work, in particular, among the recent industrial robots usedfor industrial purposes, movable robot units, such as a vertical shaftcapable of vertically movement relative to a robot base unit, ahorizontal robot upper arm and a horizontal robot forearm, are formed inhollow component structures, and drive sources for driving the shaft,the horizontal arms and a robot wrist attached to the extremity of thehorizontal arm, transmission mechanisms, reduction gear mechanisms,wiring and piping are housed within the hollow component structures toprevent the horizontal articulated robot from generating dust and oilduring operation.

However, when handling a weight such as a workpiece with a robot hand ora tool attached to the extremity of a wrist, a tensile load and abending load act inevitably on the robot arms, and the influence of thetensile and bending loads on the robot arms formed in hollow structuresis more significant than on robot arms formed in rigid structures. Thisinfluence on the robot arms cannot be entirely disregarded when thehorizontal articulated robot is applied to precision assembling work.

DISCLOSURE OF THE INVENTION

Accordingly, an object of the present invention is to provide an armstructure for an industrial robot, capable of mitigating the influenceof a load acting as the above-mentioned tensile load and bending load.Another object of the present invention is to provide a horizontalmulti-articulate type industrial robot having a light weight and able toresist the tensile and bending loads.

In accordance with the present invention, there is provided anindustrial robot comprising a vertical robot shaft, a first robot armattached to the upper end of the vertical robot shaft,transmission-reduction gear means fixedly provided on the free end ofthe first robot arm and contained in a case, a second robot armpivotally joined to the free end of the first robot arm, a plurality ofcoupling bolt means each penetrating through the interior of the firstrobot arm, and having one end fixed to the case containing thetransmission-reduction gear means and the other end projecting from andfixed to the rear end of the first robot arm, and fastening nut meanseach engaging at least one end of each of the coupling bolt means,wherein a compressive force is applied beforehand to the first robot armwhen coupling the transmission-reduction gear means with the first robotarm.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and advantages of the present invention willbe described in detail hereinafter with reference to a preferredembodiment thereof illustrated in the accompanying drawings.

FIG. 1 is a fragmentary perspective view of a horizontalmulti-articulate type industrial robot incorporating an arm structure,in a preferred embodiment according to the present invention; and

FIG. 2 is a sectional view taken along the line II--II in FIG. 1.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIGS. 1 and 2 showing the essential portion of a horizontalarticulated industrial robot incorporating an arm structure according tothe present invention, the industrial robot 10 has a swiveling body 12.The swiveling body 12 is a component capable of swiveling about avertical axis relative to a bed, not shown, in directions indicated bydouble-headed arrow θ. A vertical shaft 14 is mounted for verticalmovement in directions indicated by a double-headed arrow Z on theswiveling body 12. A first arm 16 included in a horizontal robot armstructure is attached to the top of the vertical shaft 14 so as toextend horizontally to the front. A transmission-reduction gear box 18comprising a transmission-reduction gear and a case containing thetransmission-reduction gear is attached to the free end of the first arm16. A second arm 20 included in the horizontal arm structure is attachedto the lower part of the transmission-reduction gear box 18 for aturning motion in a horizontal plane about a vertical axis in directionsindicated by a double-headed arrow U so as to extend horizontallysimilarly to the first arm 16. Although not shown in the drawings,ordinarily a robot wrist is provided on the free end of the second arm20 for handling various loads through robot actions. A motor, not shown,for the turning motion of the second arm 20 is housed in the first arm16. The output of the motor is transmitted through thetransmission-reduction gear, not shown, contained in thetransmission-reduction gear box 18 and including, for example, a skewgear mechanism for the second arm 20, to drive the second arm 20 for aturning motion within a horizontal plane.

According to the present invention, the transmission-reduction gear box18 is joined to the free end of the first arm 16 with a plurality ofelongated coupling bolts 22, and each coupling bolt 22 has one end 22aprojecting from the rear end of the first arm 16 and fastened to therear end of the first arm 16 with a fastening nut 24, and the other endprojecting to the front from an appropriate flange 18a formed in the endsurface of the transmission-reduction gear box 18 and fixed to the frontface of the flange 18a with a fastening nut 26.

That is, the elongated coupling bolts 22 are extended through theinterior of the first arm 16 and the respective opposite ends of theelongated coupling bolts 22 are fastened to the opposite ends of thefirst arm 16 to preload the first arm 16 by applying a compressive forcebeforehand to the first arm 16. Accordingly, when the robot 10 holds aload by means of the robot wrist provided on the free end of the secondarm 20 for robot actions, and thereby the long first arm 16 is subjectedto a tensile force and a bending moment caused by the load, thecompressive force applied beforehand to the first arm 16 suppresses theinfluence of the tensile force and the bending moment on the first arm16. When a component similar to the transmission-reduction gear box 18is provided on the extremity of the second arm 20, the second arm 20 maybe provided with the same construction for preloading the second arm 20by applying a compressive force to the second arm 20 as that forapplying beforehand the compressive force to the first arm 16, to effectboth coupling such a component to the second arm 20 and preloading thesecond arm 20 by a compressive force.

Although the coupling bolts 22 provided on the first arm 16, in theembodiment described hereinbefore, are fastened at the respectiveopposite ends thereof to the first arm 16 with the fastening nuts 24 and26, respectively, each coupling bolt 22 may be provided with a bolt headat one of the opposite ends 22a and 22b thereof and may be fastened tothe first arm 16 at the other end with the fastening nut 24 or 26.Furthermore, when the first arm 16 has a rectangular cross section, itis preferable to extend the coupling bolts 22 respectively along thefour internal corners and contiguously with the internal wall surfacesof the first arm 16 as shown in FIG. 2 to secure sufficient internalspace 27 for wiring and piping to enable the application of a sufficientlongitudinal compressive force to the first arm 16. Still further, whenthe first arm 16 has a circular cross section, it is desirable toarrange the plurality of coupling bolts 22 along the internalcircumference of the first arm 16 at regular angular intervals.

As apparent from the foregoing description, the arm structure of anindustrial robot according to the present invention employs elongatedcoupling bolts for attaching a transmission-reduction gear box to oneend of an arm, and the coupling bolts are extended through the interiorof the arm and are fastened to the arm so as to preload the arm by acompressive force. Therefore, the influence of a tensile force andbending moment caused by a load on the arm can be satisfactorilyreduced. Naturally, the present invention is also applicable to therespective arms of other articulated type industrial robots, not tomention the horizontal multi-articulated type industrial robot asspecifically described herein with reference to the preferred embodimentthereof.

We claim:
 1. An industrial robot comprising: a vertical robot shaft; afirst robot arm secured to an upper end of said vertical robot shaft;transmission-reduction gear means secured to a free end of said firstrobot arm and contained in a case; a second robot arm pivotally joinedthrough said transmission-reduction gear means to the free end of saidfirst robot arm; a plurality of coupling bolts, each bolt extendingthrough the interior of said first robot arm and having one end securingsaid case containing said transmission-reduction gear means to saidfirst robot arm and the other end projecting from and fastened to a rearend of said first robot arm; and a fastening nut engaging at least oneend of each of said coupling bolts, wherein said nuts are tightened onsaid bolts to couple said transmission-reduction gear means to saidfirst robot arm and compress said first arm.
 2. An industrial robotaccording to claim 1, wherein said fastening nuts are fastened to saidcoupling bolt means at the rear end of said first robot arm.
 3. Anindustrial robot according to claim 1, wherein said first robot arm iscomprised of a hollow structure having a rectangular cross section. 4.An industrial robot according to claim 3, wherein said plurality ofcoupling bolts comprise four elongated bolts, and said four bolts extendthrough said first robot arm respectively along four corners of saidfirst robot arm.
 5. An industrial robot according to claim 1, whereinsaid first robot arm is formed in a hollow structure having a circularcross section, and said plurality of coupling bolt means areequiangularly arranged along the circumference of a wall of said firstrobot arm.
 6. An industrial robot according to claim 1, wherein saidfirst and second arms are horizontal articulated arms disposed in ahorizontal position relative to said vertical axis.